Microscopic model for photoinduced magnetism in the molecular complex [Mo(IV)(CN)(2)(CN-CuL)(6)](8+) perchlorate

A theoretical model for understanding photomagnetism in the heptanuclear complex [Mo(IV)(CN)(2)(CN-CuL)(6)](8+) perchlorate is developed. It is a many-body model involving the active orbitals on the transition metal ions. The model is exactly solved using a valence bond approach. The ground state solution of the model is highly degenerate and is spanned by five S=0 states, nine S=1 states, five S=2 states, and one S=3 state. The orbital occupancies in all these states correspond to six Cu(II) ions and one diamagnetic Mo(IV) ion. The optically excited charge-transfer (CT) state in each spin sector occurs at nearly the same excitation energy of 2.993 eV for the physically reasonable parameter values. The degeneracy of the CT states is largest in the S=3 sector and so is the transition dipole moment from the ground state to these excited states. Thus laser irradiation with light of this energy results in most intense absorption in the S=3 sector. The lifetime of the S=3 excited states is also expected to be the largest as the number of states below that energy is very sparse in this spin sector when compared to other spin sectors. These twin features of our model explain the observed photomagnetism in the [Mo(IV)(CN)(2)(CN-CuL)(6)](8+) complex.